The present invention relates to a light-to-light conversion method for storing information contained in electromagnetic radiation signals such as light signals in the form of a corresponding pattern of electric charges and for reading out, with high resolution, in the form of electromagnetic signals, and also relates to a high resolution display unit for reducing the method in practice. More particularly, the present invention relates to the improvements in and relating to a signal conversion system for converting time sequential signals to two-dimensional signals.
There are known various display units, such as cathode ray tubes, liquid crystal panels, plasma display panels, projection cathode ray tubes, liquid crystal projectors, etc. As a high resolution display system, there has been proposed a modified display unit wherein picture information is written to a spatial light modulation means which in turn modifies the incident light to display an image.
Such conventional high resolution display unit is shown in FIG. 6 of the accompanying drawings. The display unit 10 includes a dielectric mirror 12 laminated between a photoconductive layer 14 and a photo-modulation layer 16. The outside surfaces of the respective layers 14, 16 are laminated with a pair of transparent electrodes 18, 20 across which a voltage is applied by a power supply 22 when the recorded signals are to be read. A screen 24 is disposed on the display side of the display unit 10.
The dielectric mirror 12 of the display unit 10 is provided for reflecting the incident light. Writing light containing information is projected in a time sequential manner onto the photoconductive layer 14 in a direction indicated by the arrow F1. The writing light is scanned in a direction indicated by the arrow F2, as in the television, whereby the entire incident surface of the display unit 10 receives the writing light. In this instance, pairs of electrons and holes are produced in the photoconductive layer 14 depending on the intensity of the incident light, which electron and hole pairs are then separated by a voltage applied by the power supply 22. The photo-modulation layer 16 produces an electro-optic effect under the influence of an electric field produced by the photoconductive layer 14. The electro-optic effect thus produced is exerted on the incident light.
The conventional display unit 10 of the foregoing construction operates as follows. Writing light which contains the necessary information in a time sequential manner is directed onto the display unit 10 from left to right of FIG. 6, as indicated by the arrow F1. Then, the writing light is scanned in the direction as indicated by the arrow F2. With this scanning, pairs of electrons and holes pairs are produced and then separated in the photoconductive layer 14 of the display unit 10, in the manner as described above. As a consequence, a pattern or image of electric charges is formed on the surface of the photoconductive layer 14 facing the photo-modulation layer 16.
The electron and hole pairs are produced depending on the intensity of the incident light, namely the contents of information contained in the writing light. Accordingly, the electric charge pattern thus produced corresponds to two-dimensional information which has been obtained by arranging the time sequential information arranged in the scanning direction of the writing light. The writing light moving in the photoconductive layer 14 is reflected by the dielectric mirror 12.
To read the time sequential information thus written, reading light is projected onto the whole surface of the photo-modulation layer 16 from the direction indicated by the arrow F3 shown in FIG. 6. The electric charge pattern formed in the photoconductive layer 14 produces a corresponding electric field in the photo-modulation layer 16. Under the influence of the electric field formed by the electric charge pattern or image, the photo-modulation layer 16 exerts an electro-optic effect on the incident light.
The reading light moving in the photo-modulation layer 16 in the manner described above is modified under the electro-optic effect. The reading light thus modulated is reflected by the dielectric mirror 12 and outputted in a direction indicated by the arrow F4.
The depth or degree of modulation at a particular point corresponds to the strength of the electro-optic effect at that point of the photo-modulation layer 16. Since the electro-optic effect corresponds to the electric charge pattern or image formed in the photoconductive layer 14, and since the electric charge pattern corresponds to the contents of information contained in the writing light, the modulated light reflected in the direction of the arrow F4 necessarily contains the time sequential information in the form of two-dimensional information.
The modified light is projected on the screen 24 where the time sequential information is reproduced as the two-dimensional information. To erase the information stored in the display unit 10, erasing light is projected onto the photoconductive layer 14 in a direction indicated by the arrow F5.
In the foregoing display unit 10, pieces of information are written in sequence as the writing light is scanned. On the other hand, read-out of the information is achieved two-dimensionally, i.e., all pieces of information are read out simultaneously from the entire surface of the display unit 10.
As a consequence, the display time or duration differs between an upper part and a lower part of the screen with the result that a brightness gradient or shading is produced in the reproduced image. In other words, the quantity of light gradually increases toward the upper part of the reproduced image and decreases toward the lower part of the reproduced image.
One solution for the foregoing problem is proposed in the specification of Japanese patent application No. 63-36775. According to this solution, a stripe electrode is provided for each scanning line of the writing light. When one scanning line is being scanned with the writing light, erasing light is irradiated to the preceding scanning line for erasing information recorded thereon.
In other words, the writing light is scanned to write information while at the same time the erasing light follows the writing light with a delay equal to the scanning duration for one scanning line so as to erase the recorded information. With this arrangement, the display time is substantially uniform throughout the entire region of the reproduced image.
The foregoing proposed solution however needs an additional deflection scanning system for scanning the erasing light. Furthermore, the stripe electrodes each provided for one scanning line require a precision processing which is time consuming and incurs an additional cost. Another drawback is that the resolution of the display unit is limited by the number of stripe electrodes.